Nucleic acid is formed from nucleotide bases, e.g., uracil (U) cytidine (C), adenine (A), thymine (T) and guanine (G), formed as a single-stranded linear molecule. Such a linear molecule can form a hybrid complex, or double-stranded molecule (also called a duplex), with another linear molecule by forming specific base pairs, e.g., between A and T, A and U, or G and C. Such paired molecules are called complementary molecules.
Nucleic acid hybridization is a method in which two single-stranded complementary molecules form a double-stranded molecule. This method is commonly used to detect the presence of one single-stranded molecule in a sample (the target nucleic acid) by use of a labelled probe formed of a complementary single-stranded molecule. For example, Muran et al., WO 87/04165, published Jul. 16, 1987, describe a probe having a single-stranded region complementary to the nucleic acid to be detected, and a double-stranded region having a non-radioactive label. The general uses and design of nucleic acid probes are well known in the art, see e.g., Mifflin 35 Clin. Chem. 1819, 1989, and Matthews and Kricka, 169 Anal. Biochem. 1, 1988.